Our understanding of ovarian function revolves around the events orchestrated by the gonadotropins follicle stimulating hormone (FSH) and luteinizing hormone (LH). In mammals, FSH secretion stimulates estrogen production and establishes LH reponsiveness in granulosa cells. In contrast, the LH surge initiates the periovulatory interval during which progesterone synthesis increases and granulosa cell proliferation largely decreases. Data now exist to suggest that luteinization in vitro is associated with a burst of proliferation prior to cell cycle arrest. This proliferative burst coincides with a transient increase in estrogen production. This application hypothesizes that early events (<12hrs) following an ovulatory stimulus are critical for ovulation and corpus luteum formation. It is specifically hypothesized that the steroid hormone estrogen regulates aspects of these early events and is necessary for the formation of a functional corpus luteum in primates. Studies will a) define the early periovulatory events occurring within 12hrs of an ovulatory stimulus in vivo and b) discern a role for estrogen in modulating early periovulatory events in vitro. We expect to demonstrate a proliferative burst in vivo, supported by mitogenic effects of estrogen on granulosa cells. [unreadable] [unreadable]